太赫兹场作用下半导体超晶格的动力学过程及光吸收谱研究

Dynamical process and optical absorption spectra of semiconductor superlattice under terahertz field

基于激子基,采用密度矩阵理论研究了太赫兹场作用下半导体超晶格的子带间动力学过程及光吸收谱。在太赫兹场的驱动下,激子作布洛赫振荡。子带间极化的缓慢变化依赖于太赫兹频率,随着太赫兹频率的增加,子带间极化向下振荡,极化强度降低。以In_(0.52)Al_(0.48)As/InAs和Ga_(0.7)Al_(0.3)As/GaAs两种超晶格为例进行研究,它们的光吸收谱出现了卫星峰结构,这是由于太赫兹场与万尼尔斯塔克阶梯激子作用的非线性效应产生的。但是就In_(0.52)Al_(0.48)As/InAs与Ga_(0.7)Al_(0.3)As/GaAs超晶格相比而言,研究发现,n<0的激子态与n=0的激子态耦合作用较强,使得光吸收谱吻合性较好,n=0时的激子态吸收光谱出现红移,n>0的激子态光吸收谱中出现的边带效应不是很明显。

Based on an excitonic basis, the intraband dynamical process and optical absorption spectrum of semiconductor superlattice in terahertz fields are investigated with the density matrix theory. The excitonic Bloch oscillation is driven by the terahertz field. The slow variation in the intraband polarization depends on the terahertz frequency. With the increase of terahertz frequency, the intraband polarization does oscillate downwards and its intensity decrease. Taking In0.52Al0.48As/InAs and Ga0.7Al0.3As/GaAs superlattices for examples, because of the nonlinear effect of terahertz field and WSL excitons, their optical absorption spectra take on satellite peak structures. However, when these two superlattices in different states are compared, it＇s concluded that the optical absorption spectrum anastomoses well for the strong coupling effect between the excitonic state of n 〈 0 and the state of n =0, while a red shift emerges in the state of n = 0 and the sideband effect in the optical absorption spectrum is not very obvious in the state of n 〉 0.